Showing papers on "Particle published in 1973"
TL;DR: In this article, a series of monodisperse suspensions of the same chemical composition but of rather different particle sizes was used to study particle size dependent phenomena, such as Brownian motion, light scattering, sedimentation and electrophoresis of small particles.
Abstract: MANY properties of colloids and suspensions depend on the particle size. Series of monodisperse suspensions of the same chemical composition but of rather different particle sizes may be used to study particle size dependent phenomena, such as Brownian motion, light scattering, sedimentation and electrophoresis of small particles. We have used such series to demonstrate the increased tendency of metal suspensions to coagulate in the presence of electrolytes as the radius of the particles increases1.
7,739 citations
TL;DR: In this article, a simple light scattering technique was used to obtain the relative rates of flocculation and optimum flocculant concentrations, under given conditions the optimum concentration was independent of the molecular weight of the polymer.
412 citations
TL;DR: In this article, the ionic strength of the aqueous phase was found to play an important part in determining particle size; this was explained in terms of a limited coagulation process occurring at the stage involving the nucleation of polymer particles.
Abstract: Methods have been devised for the formation of monodisperse polystyrene latices in the absence of added surface active agents. The particles are stabilised, as a colloidal dispersion, by surface groupings which are an integral part of the particle and are not removed by dialysis. By suitable variation of the ionic strength of the aqueous phase, the initiator concentration and the polymerisation temperature, the final particle size obtained in single-stage reactions was varied between c. 0.15 and 1.0 μm. The coefficient of variation on particle diameters was usually less than 5%. The ionic strength of the aqueous phase was found to play an important part in determining particle size; this was explained in terms of a limited coagulation process occurring at the stage involving the nucleation of polymer particles. Conductometric titration experiments revealed the presence of sulphate, carboxyl and hydroxyl groups on the particle surfaces. Molecular weight determination of the polystyrene formed showed that this was lower than that formed in conventional emulsion polymerisation.
248 citations
01 Aug 1973
TL;DR: In this paper, the thermophoretic velocity, vth, was related to the particle and liquid properties by an expression similar to Epstein's gas equation: V th =-0.26 kμ 2k+k p ρT ▽T.
Abstract: Experimental evidence of thermophoresis in liquids is reported for 1.011 and 0.790 μm latex spheres in water and n-hexane. The thermophoretic velocity, vth, was related to the particle and liquid properties by an expression similar to Epstein's gas equation: V th =-0.26 kμ 2k+k p ρT ▽T .
237 citations
01 Mar 1973
TL;DR: In this paper, the equilibrium aspects of weak flocculation have been investigated using model dispersions, and an attempt has been made to correlate this critical particle concentration with the depth of the energy minimum in the particle interaction curves.
Abstract: The equilibrium aspects of weak flocculation have been investigated using model dispersions. Direct particle counting techniques from photomicrographs, and turbidity-wavelength measurements have been used to characterize the degree of flocculation as a function of particle concentration in the dispersions. The results indicate a critical particle concentration, below which the system is stable, and above which flocs appear tc be in equilibrium with singlet particles. An attempt has been made to correlate this critical particle concentration with the depth of the energy minimum in the particle interaction curves.
188 citations
01 Mar 1973
TL;DR: Theoretical predictions of particle capture from suspensions flowing around spherical, rotating disc and cylindrical collectors are presented in this paper, which are intended to describe collection of non-Brownian particles under negligible double layer forces from water, primarily for application to deep bed filtration.
Abstract: Theoretical predictions of particle capture from suspensions flowing around spherical, rotating disc and cylindrical collectors are presented. These results are intended to describe collection of non-Brownian particles under negligible double layer forces from water, primarily for application to deep bed filtration. The predictions are obtained from numerical solutions of the trajectory equations of Spielman and Goren for motion of a small particle near a much larger collector with hydrodynamic, gravitational and London-van der Waals forces considered simultaneously. Electrical double layer forces are introduced only to establish a criterion for their neglect. Comparison with experiment is presented in a subsequent paper.
162 citations
Patent•
06 Aug 1973
TL;DR: An electric arc plasma spray gun provides optimum coating of substrates by projecting a stream of plasma at a velocity at or about Mach 2, at ambient pressure, and entraining therein particles of material to be coated upon said substrate.
Abstract: An electric arc plasma spray gun provides optimum coating of substrates by projecting a stream of plasma at a velocity at or about Mach two, at ambient pressure, and entraining therein particles of material to be coated upon said substrate. Power, pressures and temperatures are employed together with a unique set of interchangeable supersonic nozzles to achieve particle exit velocities of from one to ten thousand feet per second, heating said particles to a temperature below their melting point but sufficient to soften the particles for enhanced coating. Unique parameters of particle size, particle injection angle and particle injection positions are identified for different materials to be entrained in the supersonic plasma stream.
139 citations
TL;DR: A theory of particle formation based on a model involving initiation of free radicals in the continuous medium and self-nucleation or particle capture is proposed in this paper, where expressions for determining the number of particles are presented together with a consideration of limiting cases.
Abstract: A theory of particle formation based on a model involving initiation of free radicals in the continuous medium and self-nucleation or particle capture is proposed. Expressions for determining the number of particles are presented together with a consideration of limiting cases.
138 citations
TL;DR: In this article, a technique for the direct preparation of polymer dispersions of controlled particle size in organic media is described, which involves the polymerisation of a monomer dissolved in an organic liquid to produce insoluble polymer dispersed in the continuous phase.
Abstract: The development of a technique for the direct preparation of polymer dispersions of controlled particle size in organic media is described. This method of dispersion polymerisation involves the polymerisation of a monomer dissolved in an organic liquid to produce insoluble polymer dispersed in the continuous phase. An amphipathic graft or block copolymer is used as the dispersant. The general features of the process, including the method used for stabilising the polymer dispersions and the mode of particle formation and growth, are reviewed.
136 citations
TL;DR: In this article, it was shown that there is no effect of particle drag when instability sets in, although the rate at which unstable perturbations grow is affected by this factor.
Abstract: In the simplified case considered, particles decrease the critical temperature difference for the onset of convection by increasing the heat capacity of the fluid. A proof of exchange of stabilities shows that there is no effect of particle drag when instability sets in, although the rate at which unstable perturbations grow is affected by this factor. Thermal force alone can, in principle, give rise to instability in layers heated from above or below. The results are discussed with reference to experiments in gas‐particle mixtures which show “columnar instabilities” at unusually low‐temperature differences.
130 citations
TL;DR: In this paper, a linear array of particles with different sizes was treated quantitatively; number, rather than weight, distributions are considered directly to permit summation of particle-pair interactions.
Abstract: Diffusion models for the initial-stage sintering of spherical particles were developed for distributions of particle sizes. A linear array of particles with different sizes was treated quantitatively; number, rather than weight, distributions are considered directly to permit summation of particle-pair interactions. Evaluation of a single particle size which will characterize the equivalent shrinkage of the distributed array of random particles yields a size much smaller than that which would designate the division at 50 wt% finer conventionally used. Also, the effective size is smaller for the lattice-diffusion model than for the grain-boundary-diffusion-controlled model. The results show that the rates for binary mixtures are intermediate between the behaviors of the end-member sizes, in accordance with previous experimental findings. A square array of equal spheres with contacting interstitial spheres was also analyzed. Coherent shrinkage requires a retardation of shrinkage along the diagonal contacts (due to tensile loads). Procedures for evaluating the stress transfer were generated for this and similar particle packings. The calculated shrinkage rate is again intermediate between that predicted from previous models and the end-member sizes.
TL;DR: Particles occurred at highest concentrations in the dorsal sacs of the rumen and responded to effects of time and level of feeding; smaller particles showed less response, and the density of coarse particles tended to he low and that of fine particles tcnded to be high.
Abstract: 1. Three cows were given 3, 5 or 7 kg hay once daily in a Latin-square design, and samples of digesta from four sites in the rumen and one site in the reticulum were taken at six times within the 24 h period after the feed. Dry-matter content and distribution of particle size and of particle density were measured for each sample. The changes in these measurements with time were studied. The incidence of rumination was also recorded.2. Dry-matter contents of samples ranged from 15 to 3%. Values for samples from the dorsal sacs of the rumen were considerably higher than those for samples from the ventral sites; they also changed more with time after feeding and with level of feeding.3. Particles were fractionated by sieving into six size groups with mean dimensions (mm) of 9·3 × 0·8, 4·4 × 0·6, 2·6 × 0·3, 1·6 × 0·25, 0·5 × 0·1 and smaller than 0·5 × 0·1. Coarse particles occurred at highest concentrations in the dorsal sacs of the rumen and responded to effects of time and level of feeding; smaller particles showed less response.4. Particle densities ranged from 800 g/l to 1500 g/l. The proportions of low-density particles were higher in samples from the dorsal sacs of the rumen than in samples from ventral sites; the latter samples had higher proportions of high-density particles than of low-density particles. The changes which occurred are discussed.5. The density of coarse particles tended to be low and that of fine particles tended to be high.6. Rumination started at the time of maximum concentration of particles of low density and minimum concentration of particles of high density. Conversely, rumination ended when the concentration of the low-density particles was a minimum and that of the dense particles a maximum.7. The results are discussed in relation to the possible movement of particles within the reticulo-rumen and the kinetics of particle breakdown.
01 Nov 1973
TL;DR: In this paper, the nonequilibrium state of the probability distribution of orientations of nonspherical axisymmetric rigid particles is derived for a dilute suspension subjected to a simple shear flow assuming no particle interactions and negligible Brownian motion.
Abstract: The nonequilibrium state of the probability distribution of orientations of nonspherical axisymmetric rigid particles is derived for a dilute suspension subjected to a simple shear flow assuming no particle interactions and negligible Brownian motion. If the particles in the suspension are initially oriented randomly, the orientation distribution function undergoes undamped oscillations of frequency twice that of a particle rotation about the vorticity axis. Thus the instantaneous rheological properties of the suspension, such as the intrinsic normal stress differences and the intrinsic viscosity which are obtained as averages with respect to orientation, should also oscillate with time. Experiments on sheared suspensions of rigid rods and discs have shown that the orientation distribution does oscillate but is damped, dying away to an equilibrium distribution which may then proceed to change slowly with time. Two possible causes for this damping are considered, the first being the slight variation in shape between particles and the second, the changes in orientations resulting from 2-body interactions. In both cases, the rotating particles experience changes in rotational phase which lead eventually to the equilibrium distribution of orientation and of the associated rheological properties. It is predicted that the systems are non-Newtonian in the nonequilibrium state except when the equivalent axis ratio is unity (corresponding to spheres), but Newtonian in the equilibrium state. Each mechanism has its own relaxation time for which approximate equations are derived.
TL;DR: The structure of β-hydride precipitated in the b.c. matrix of hydrogen charged vanadium has been studied by electron diffraction in conjunction with electronmicroscopy.
TL;DR: In this paper, an ordered state where spins are coupled with their directions statistically distributed within a very fine particle was found, and the spin structure is quite different from normal antiferromagnetism.
Abstract: AMORPHOUS materials have no preferred crystal axes, but it might be thought that shape or strain could define an antiferromagnetic axis in a compound containing a large concentration of magnetic ions with negative nearest-neighbour exchange interactions. We have studied such an amorphous compound, and find an ordered state where spins are coupled with their directions statistically distributed within a very fine particle. This spin structure is quite different from normal antiferromagnetism, although there are some similarities in the magnetic properties.
TL;DR: In this paper, the motion of small particles entrained in a free argon plasma jet was studied by means of high-speed cine streak photography, and the system was found to be characterized by low relative Reynolds numbers (0.2 to 20) and extremely high deceleration rates (about 2,000 g).
Abstract: The motion of small particles (glass microspheres, 30 to 140 microns in diameter) entrained in a free argon plasma jet was studied by means of high-speed cine streak photography. Radial temperature and velocity profiles as well as axial profiles of temperature, velocity, and argon concentration in the jet were experimentally determined by means of a plasma calorimetric probe. The system was found to be characterized by low relative Reynolds numbers (0.2 to 20) and extremely high deceleration rates (about –2,000 g). Under these conditions, an increase of drag coefficient over that predicted by the standard curve was experimentally observed. This increase was attributed to the nonsteady flow field around the particle (the so-called “history term” in the equation of motion). A general computer program has been proposed which predicts the particle velocity, acceleration and temperature along its trajectory.
TL;DR: In this article, conditions for the formation of copper hydrous oxide dispersions of uniform size and shape are described, and the results show that these particles show cubic crystal symmetry characteristic of Cu 2 O, although their habit changes from cubic, through cuboctahedral to octahedral as the average particle size increases.
TL;DR: In this article, the authors discussed some of the parameters which affect the phenomenon of segregation in mixtures of coarse and fine particles when subjected to vibration and found that acceleration was the most critical external variable affecting segregation phenomena.
TL;DR: In this paper, the trajectory equations for non-Brownian particle motion in flow past spherical and rotating disc collectors are solved numerically to yield prediction of particle collection when particle-collector interactions are of the classical colloid type (DLVO).
TL;DR: In this paper, a model of boron ignition treating the inhibiting effect of a boric oxide coating has been developed, converted to difference form and programmed for computer solution for determination of ignition limits and ignition times.
Abstract: A model of boron ignition treating the inhibiting effect of a boric oxide coating has been developed. Transient differential equations describing the generation and removal of the oxide and associated thermal effects along with heat transfer between the particle and surroundings have been derived, converted to difference form and programmed for computer solution for determination of ignition limits and ignition times. Predictions for particles studied by Macek in a flat-flame burner have been compared with experimental results—agreement is good for dry gas cases, but poor when the gas stream includes water. The program has been used to predict effects of initial oxide thickness, particle size, pressure, oxygen content, initial particle temperature, gas temperature and surroundings radiation temperature on ignition. In addition, the original differential equations have been treated by a stability analysis to determine ignition limits—excellent agreement is found between results obtained with the stability ...
01 Mar 1973
TL;DR: In this paper, the effect of compaction on the specific surface area and pore structure of yttria stabilized powders has been studied by measuring adsorption isotherms of nitrogen at −196°C.
Abstract: Silica and zirconia (yttria stabilized) powders with an extremely small particle size (∼40 A) and a narrow size distribution have been prepared by a vapor-phase condensation process which gave no strong particle agglomeration. The effect of compaction, over a pressure range up to 100 tons in−2, on the specific surface area and pore structure of these powders has been studied by measuring adsorption isotherms of nitrogen at −196°C; marked decreases in surface area, pore size and total pore volume occurred. The results are in close accord with a structural model for the compacts, consisting of regularly packed spherical particles with a coordination number controlled by the extent of compression. At the highest pressures of compaction Type I isotherms were obtained, an indication that with pores below some critical radius-estimated from the Kelvin equation as r - 17 A, the capillary condensation mechanism is no longer operative.
TL;DR: For a number of solvents, the effective hard sphere diameter at several temperatures is determined from gas solubility data using the expression of the scaled particle theory of the work of cavity formation as mentioned in this paper.
Abstract: For a number of solvents, the effective hard sphere diameter at several temperatures is determined from gas solubility data using the expression of the scaled particle theory of the work of cavity formation. From the results, the linear coefficients of expansion l1 of the effective hard core diameter are calculated and discussed in relation to values determined by other methods.
TL;DR: In this paper, a technique for the computer simulation of the motion of 10,000 simulated molecules is described, where the number of computer operations per time-step is proportional to the number simulated particles even though the force of interaction may be long range and no force cut-off is employed.
TL;DR: In this article, the optical absorption produced by small (10-100 A) silver particles in a glass matrix has been studied, and it has been shown that the width of the absorption correspond to those calculated theoretically using the particle sizes estimated from electron microscopy, whilst the peak position of the absorbance calculated for the smallest size particles does not seem to be so reliable.
01 Jan 1973
TL;DR: The 6th ESLAB Symposium as discussed by the authors was held in Noord wijk from 26-29 September 1972 with the theme "Photon and Particle Interactions with Surfaces in Space." More than 60 scientists attended mainly from ESRO Member States and from America.
Abstract: The 6th ESLAB Symposium, organised by the Space Science Department (formerly ESLAB) of the European Space Research and Technology Center, was held in Noord wijk from 26-29 September 1972. This year the theme was "Photon and Particle Interactions with Surfaces in Space." More than 60 scientists attended mainly from ESRO Member States and from America. The first part of the Symposium was devoted to introductory lectures and to papers on interactions with spacecraft. The second half dealt with the photon and particle interactions with celestial objects, and ended with a general discussion and presenta tions of areas where new developments are required. The purpose of this Symposium was to throw light on the importance of the prob lems which are evoked by E. A. Trendelenburg in his introductory remarks, and to sum up our present understanding of these phenomena. It is hoped that this book will prove useful to physicists and engineers who are actually involved in space ex periments and are concerned with interactions of these types. R. J. L. GRARD OPENING ADDRESS Gentlemen, I should like to welcome you to the 6th ESLAB Symposium. In the past we have always organised this Symposium jointly with our sister in stitute, ESRIN, in Frascati, but unfortunately reductions in the scientific budget have forced ESRO to terminate the activities of that laboratory. Nevertheless, we have decided to carryon the tradition, and we shall continue on our own organising this series of symposia on specialised subjects."
TL;DR: The infrared spectral reflectance of a semi-infinite medium composed of irregular particles of different materials is calculated in terms of the sizes, shapes, and complex refractive indices of the particles.
Abstract: The infrared spectral reflectance of a semi-infinite medium composed of irregular particles of different materials is calculated in terms of the sizes, shapes, and complex refractive indices of the particles. For particles larger than the wavelength, the scattering and absorption are computed mainly by geometrical optics but with important wave-optical corrections for the additional absorption caused by edges and asperities, which are represented by dipoles distributed over the surface of the particle. For particles smaller than the wavelength, a Lorentz-Lorenz model is used to derive the average complex index of the medium, the particles being treated as ellipsoids with a wide range of shapes. The average scattering of an individual ellipsoidal particle is then found from the relative refractive index of the particle with respect to the Lorentz-Lorenz medium. For both large and small particles the single-particle scattering is represented by six discrete beams. Calculation of the reflectance is then facilitated by a radiative transfer method that also involves six beams. For particles of intermediate size a suitable formula bridging the results for large and small particles is found to be satisfactory.
TL;DR: Two models for vertical pneumatic conveying, a uniform flow model at high gas velocities and an annular flow model near the particle terminal velocity, have been examined theoretically.
Abstract: Two models for vertical pneumatic conveying, a uniform flow model at high gas velocities and an annular flow model near the particle terminal velocity, have been examined theoretically. The uniform flow model leads to the following relationship between gas and particle velocity and line porosity:
No simple analytical solution was found for the annular flow model but a numerical solution was possible.
Both models indicate that slip velocity may exceed the particle terminal velocity under certain conditions. The theoretical predictions agree reasonably well with experimental observations.
TL;DR: The use of RELATIVE DENSITY CORRELATIONS based on an "AVERAGE" SAND to PREDICT SOIL BEHAVIOR without considering the Particle Shape can result in poor or misleading predictions.
Abstract: THE USE OF RELATIVE DENSITY CORRELATIONS BASED ON AN "AVERAGE" SAND TO PREDICT SOIL BEHAVIOR WITHOUT CONSIDERING THE PARTICLE SHAPE CAN RESULT IN POOR OR MISLEADING PREDICTIONSEXPERIMENTAL DATA SHOW THAT THE PARTICLE SHAPE HAS A PRONOUNCED EFFECT ON ALL ENGINEERING PROPERTIES STUDIEDANGULARITY OF THE PARTICLES INCREASES THE MAXIMUM VOID RATIO, STRENGTH, AND DEFORMABILITY OF COHESIONLESS SOILSVARIATIONS IN ENGINEERING PROPERTIES DUE TO PARTICLE SHAPE CAN BE AS LARGE AS VARIATIONS ASSOCIATED WITH LARGE DIFFERENCES IN RELATIVE DENSITYPENETRATION TESTS IN SMALL CONTAINERS WITH SMALL RODS SUGGEST THAT THE STANDARD PENETRATION TEST IS INFLUENCED BY BOTH THE ANGULARITY AND DENSITY OF COHESIONLESS SOILS /AUTHOR/ ABSTRACT OF THE SYMPOSIUM IS IRRD ABSTRACT NO 210328
TL;DR: In this article, the behavior of a spherical particle in the no flow system and the laminar flow system was studied experimentally, using the square-and circular-section tube, and the mechanism of the tubular pinch effect was done on the basis of the observed results.
Abstract: The behaviour of a spherical particle in the no flow system and the laminar flow system was studied experimentally, using the square- and circular-section tube. And, the following facts became evident:
Besides, on the mechanism of the tubular pinch effect, a proposal was done on the basis of the observed results.
TL;DR: Characteristics of the particle motion allow improved volume distribution determinations by properly accounting for the shape factor, and analysis of the data indicates that the convergent entrance flow orients the cells so that they enter the pore with their axis of symmetry perpendicular to the por axis.